Analog store digital read ultrasound beamforming system and method

ABSTRACT

An analog store-digital read (ASDR) ultrasound beamformer architecture performs the task of signal beamforming using a matrix of sample/hold cells to capture, store and process instantaneous samples of analog signals from ultrasound array elements and this architecture provides significant reduction in power consumption and the size of the diagnostic ultrasound imaging system such that the hardware build upon ASDR ultrasound beamformer architecture can be placed in one or few application specific integrated chips (ASIC) positioned next to the ultrasound array and the whole diagnostic ultrasound imaging system could fit in the handle of the ultrasonic probe while preserving most of the functionality of a cart-based system. The ASDR architecture provides improved signal-to-noise ratio and is scalable.

RELATED APPLICATIONS

This application is the U.S. National Phase of International ApplicationPCT/IB2014/000281 which published as publication number WO 2014/125371on Aug. 21, 2014, which publication is incorporated herein by reference.International Application PCT/IB2014/000281 claims the benefit of U.S.Provisional Patent Application Ser. No. 61/763,929, filed Feb. 12, 2013entitled “Analog Store—Digital Read (ASDR) Ultrasound Beamformer Methodand System.”

BACKGROUND INFORMATION

1. Field of the Invention

The present invention relates to ultrasonic beamforming, morespecifically the present invention relates to an analog store, digitalread (ASDR) ultrasound beamforming system and associated method.

2. Background of the Invention

There are number of areas in the electronics field in which analogmemory devices are being used successfully such as digital storageoscilloscopes, and in the physics field X-ray and charged-particletracking applications. Some early predecessors of this technology can betraced to digital oscilloscopes and waveform capturing devices based onFast-In-Slow-Out (FISO) principle such as one described in U.S. Pat. No.4,271,488 entitled “High-Speed Acquisition System Employing An AnalogMemory Matrix” or in U.S. Pat. No. 4,833,445 entitled “FISO SamplingSystem”. These patents are incorporated herein by reference and thelatter patent depicts the fast, high resolution FISO system, while theformer describes an acquisition system that uses an analog memory matrixbuilt of sample-hold cells arranged in rows and columns to form an M×Nmatrix that may be implemented on a single integrated-circuit (IC) chip.

The idea of a matrix analog memory device on IC was further developed byStewart Kleinfielder who produced a range of multichannel transientanalog waveform digitizer chips used to capture data from detectors inneutrino physics experiments, as well as by other contributors (forexample, see Kleinfelder, S. A., “A 4096 Cell Switched Capacitor AnalogWaveform Storage Integrated Circuit”, IEEE Transactions on NuclearScience, NS-37, No. 1, February 1990.; and Kleinfelder, S. A., “AdvancedTransient Waveform Digitizers,” SPIE Particle AstrophysicsInstrumentation Proc., v. 4858, pp. 316-326, August 2002.) Additionalprior art representing informative background can be found in U.S. Pat.No. 5,722,412 entitled “Hand Held Ultrasonic Diagnostic Instrument”;U.S. Pat. No. 6,126,602 entitled “Phased Array Acoustic Systems withIntra-Group Processors”; U.S. Pat. App. Pub. No. 2008-0262351A1 entitled“Microbeamforming Transducer Architecture”; U.S. Pat. App. Pub. No.2010-0152587A1 entitled “Systems and Methods for Operating aTwo-Dimensional Transducer Array”; and U.S. Pat. APP. Pub. No.2011-0213251A1 entitled “Configurable Microbeamformer Circuit for anUltrasonic Diagnostic Imaging System.” See also Haller, G. M.; Wooley,B. A., “A 700-MHz switched-capacitor analog waveform sampling circuit,”IEEE Journal of Solid-State Circuits, v. 29(4), pp. 500-508, April 1994.The above identified patents and published patent applications areincorporated herein by reference.

In medical diagnostic ultrasound, there were a number of attempts to useanalog memory for ultrasound signal beamforming, notably U.S. Pat. Nos.6,500,120 and 6,705,995, which are incorporated herein by reference. Theprocess of ultrasound imaging, such as in medical diagnostic, beginswith sending specially constructed ultrasonic signals (pulses, waves orwave packets) into the subject, e.g., tissues in medical diagnostics (orturbine blades for jet engine inspection, etc.) The pressure pulsepropagates in depth while attenuating and scattering on the acousticimpedance interfaces (such as a boundary between different tissues)along the way. These scattered echoes are picked up by the receivingultrasound array and from this data the tissue composition along thepulse propagation path is reconstructed as a single scan line. Then, thenext pulse is sent into a different direction and the process ofreceiving scattered (or attenuated as in transmission tomography)ultrasound signals back to the sensor array, and the interpretation ofthe results is repeated until a required 2-D slice (B-mode frame) or a3-D volume is assembled out of separate scan lines.

In order to increase the spatial and contrast (magnitude) resolution ofa signal coming from the certain spatial location within the tissue, theultrasound array needs to be focused on that location. Thus, in thecourse of pressure pulse propagation in the tissue, the receiving arrayneeds to constantly shift its focus following the pulse currentposition. Therefore, one of the first steps in processing the raw datais called beamforming in which signals coming to different elements ofthe array are time-shifted before they will be added to one another. Asa rule, the beamforming applies to both, transmit and receive signals.

FIG. 1 illustrates the first method used in forming ultrasound images,also known as analog beamforming Generally, the ultrasound imagingdevice consists of an ultrasonic array 106 divided to a number ofindependent elements 107 or channels (typically to 64 or 128 elements inlinear or curved 1D array). During the transmit stage of interrogation,the transmit beamformer sends variably delayed electric pulses to theelements of the ultrasound array 106. The relative delays between thesignals is constructed in such a way that ultrasonic pulses emitted byelements 107 of the array 106 would arrive to the predetermined spatialpoint 100 (focal point P) simultaneously, with their phases aligned toachieve a coherent summation of wavelets coming from all elements 107 ofthe array 106. This wave would scatter at the point 100 and part of thisspherical scattered wave would travel back to the elements 107 of thearray 106. Each element 107 would convert pressure variations in theincoming wave into the voltage variation output 108. The portion of thisscattered wave that reaches a face surface of an array element 107 canbe seen as a wavelet 102 that travels along the ray 104 that connectsthe scattering point 100 and the face of the element 107. Depending onthe mutual position of the scattering point 100 and the specific element107 of the array 106, the path 104 would vary from the shortest oneequivalent to radius R₀ 105 to the longest one. The spatial differenceAD; between the shortest path 105 and path from the point 100 to thei-element of the array 106 translates into the time delay Δt_(i) betweenthe arrivals of signals 108. The task of the receive beamformer is tomodify the time differences between the signals 108 from all elements107 participating in beamforming and sum them in accordance with thedirections of the beamforming algorithm. For example, such a beamformingalgorithm may require removing the time delays Δt from all arrivedsignals and sum such processed signals (delay-sum algorithm), in effectfocusing the array to the point P. It can be seen that workings oftransmit and receive beamformers are mutually reciprocal, thus,describing the works of the receive beamformer is also a description ofthe solutions for the transmit beamformer.

The ways received signals are processed define the type of thebeamformer. The analog beamformer shown on FIG. 1 was a first type ofthe beamformer used to process ultrasound signals. In it signals 108were first amplified by voltage controlled amplifier (VCA) 110 tocompensate the signal attenuation, then, a delay circuit 112 was used totime shift the signals to compensate the delays in arrival, then suchaligned signals 114 were summed in analog summing circuit 116 and theoutput signal 118 was digitized by analog-digital converter (ADC) 120producing output digital signal 122 that was stored in memory and usedby the back end processor to reconstruct B-mode or Doppler images. Theadvantage of such design is the simplicity of the hardware. Thedisadvantages include poor time discrimination and low refresh rate ofthe analog design elements 112 (no dynamic beamforming) as well asirreversibility of the beamforming process such that only onebeamforming algorithm can be applied to the captured signals.

The second common type of the beamformer used in ultrasound imaging iscommonly known as the digital beamformer (see FIG. 2). In the digitalbeamformer, voltage signals 108 from the elements of the array 106 areamplified by the voltage controlled amplifier (VCA) 110 to compensatethe signal attenuation, then, the signal in each channel is digitized ata certain sampling rate by channel ADC 124 that outputs digitized signalto the memory or Firs-In-First-Out (FIFO) registers where signals areshifted in accordance with the beamforming algorithm (for example suchthat to remove arrival delay Δt), then such processed digital data 128from each participating channel are summed by digital summator 130 andoutput data 122 are written to the memory for further processing. Theadvantages of digital beamformer, such as shown in FIG. 2 are its speedand precision which allows implementation of the dynamic beamforming andthe possibility of realization of multiple beamforming strategies on thesame data volume. The disadvantage is complexity of the hardware;manifesting in larger hardware size, higher cost, and higher powerconsumption (heat generation).

For the reasons of clarity, the beamforming schematic for analog anddigital beamformers shown on FIGS. 1 and 2 was simplified by removingthe multiplexing stage. However in reality, as known to those ofordinary skill in the art, having the number of processing channels beequal to the number of the arrays' elements is a very expensiveproposition. Thus, the array can have 64, 128, 256 or greater number ofelements but the beamformer would have typically 32 or 64 channels andan analog multiplexing circuitry that would select elements of the array106 into the current aperture. Also for the same reasons, cable andsignal connectors that connect elements of array 106 to the analogfront-end electronics are not shown, even though they do affect the costand signal quality of the system.

From the description of the beamforming process it can be seen that thesignal coming from the output of the array element 107 is processedindependently from the signals coming from the other elements up to theoutput of the beamformer where all of the signals are combined. Thus,this text will refer to this signal path from the element 107 to theinput of summator 116, 130 (or 136) as a “signal path” or “beamformingchannel” or simply as “channel” 109.

As further background the international search report inPCT/IB2014/000281 identified that publications US2012-1433059 andUS2010-0331689 and U.S. Pat. Nos. 8,545,406 and 8,317,706 were ofgeneral interest to the present invention and these disclosures areincorporated herein by reference.

There remains a need in the art to reduce the size and powerrequirements of diagnostic ultrasound imaging and to utilize beamformingarchitecture to accomplish this goal.

SUMMARY OF THE INVENTION

This invention presents an Analog Store Digital Read (ASDR) ultrasoundbeamforming architecture which performs the task of signal beamformingusing a matrix of sample/hold cells to capture, store and processinstantaneous samples of analog signals from ultrasound array elementsand this architecture provides significant reduction in powerconsumption and the size of the diagnostic ultrasound imaging systemsuch that the hardware build upon ASDR ultrasound beamformerarchitecture can be placed in one or few application specific integratedchips (ASIC) positioned next to the ultrasound array and the wholediagnostic ultrasound imaging system could fit in the handle of theultrasonic probe while preserving most of the functionality of acart-based system. The ASDR architecture provides improvedsignal-to-noise ratio and is scalable.

One aspect of the present invention provides an Analog Store DigitalRead ultrasound beamforming method for an ultrasound imaging systemcomprising the steps of: i) Providing an ultrasonic array formed ofindividual ultrasonic array elements configured for transmission andreceiving; ii) Dividing the individual array elements into individualchannels, wherein each channel comprises at least one array element;iii) Creating a receiving input signal for each channel from inputsreceived from each array element of the channel; iv) Sampling eachreceiving input signal for each channel at a sampling rate and storingthe sampled data in a bank of sample-hold cells which are associatedwith that channel, wherein the bank of sample-hold cells form an analograndom access memory for the sampled receiving input signal; v)Selecting at least one sample-hold cell data from at least one channelfor each particular output time for each beamforming instance inaccordance with a beamforming algorithm; vi) Summing all of the selectedsample-hold cell data from the associated channels for the beamforminginstance forming an analog beamformed received signal sample for thebeamforming instance; and vii) Digitizing the analog beamformed receivedsignal sample.

One aspect of the present invention provides an Analog Store DigitalRead ultrasound beamforming system for an ultrasound imaging systemcomprising an ultrasonic array formed of individual ultrasonic arrayelements configured for transmission and receiving, wherein theindividual array elements are formed into individual channels, whereineach channel comprises at least one array element and each channel usesless than 40 milliwatts in operation.

One aspect of the present invention provides an Analog Store DigitalRead ultrasound beamformer for an ultrasound imaging system comprising:i) An ultrasonic array formed of individual ultrasonic array elementsconfigured for transmission and receiving, wherein the individual arrayelements are grouped into individual channels, wherein each channelcomprises at least one array element; ii) A Receiving input signalcontrol circuitry for creating receiving input signals for each channelfrom inputs received from each array element of the channel; iii) Aplurality of banks of sample-hold cells with each bank of sample-holdcells associated with one channel, wherein the beamformer is configuredfor sampling each receiving input signal for each channel at a samplingrate and storing the sampled data in one bank of sample-hold cells whichare associated with that channel, wherein the bank of sample-hold cellsform an analog random access memory for the associated sampled receivinginput signal; iv) A beamforming processor configured for selecting atleast one sample-hold cell data from at least one channel for eachbeamforming instance in accordance with a beamforming algorithm; v) Ananalog summation element for summing all of the selected sample-holdcell data from each channel for each beamforming instance and forming ananalog beamformed received signal sample for the beamforming instance;and vi) An Analog-to-Digital converter for digitizing the analogbeamformed received signal.

These and other advantages of the present invention will be clarified inthe brief description of the preferred embodiment taken together withthe drawings in which like reference numerals represent like elementsthroughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a prior art analog beamformer;

FIG. 2 is a schematic representation of a prior art digital beamformer;

FIG. 3 is a schematic representation of an Analog Store Digital Read(ASDR) ultrasonic beamformer in accordance with one embodiment of thepresent invention;

FIGS. 4A-D are schematic representation of representative Sample/HoldCells (SHC) for use in the ASDR ultrasonic beamformer of the presentinvention;

FIG. 5 is a schematic representation of an alternative SHC for use inthe ASDR ultrasonic beamformer of the present invention;

FIG. 6 is a schematic timing diagram illustrating work of theSample/Hold Cells used in the ASDR ultrasonic beamformer of the presentinvention;

FIG. 7 is a timing diagram illustrating work of the ASDR ultrasonicbeamformer of the present invention;

FIGS. 8A and 8B are alternative schematic block diagrams of transmit andreceive beamformer channel 109 in accordance with two embodiments of thepresent invention;

FIG. 9 schematically illustrates the process of writing to and readingfrom the SHC array used in the ASDR ultrasonic beamformer of the presentinvention;

FIG. 10 is a schematic representation of a receive beamformer used inthe ASDR ultrasonic beamformer of the present invention;

FIG. 11 is a schematic block diagram of a second stage Sample/Hold Cellarray in accordance with one aspect of the present invention;

FIG. 12 is a schematic composition of common arrays;

FIG. 13 is a schematic block diagram of sub-aperture transmit andreceive beamformer in accordance with one aspect of the presentinvention; and

FIG. 14 is a schematic block diagram representing an example of an ASDRultrasound system in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to ultrasound diagnostic systems, such asused in medical diagnostic systems for medical human and animalapplications. The system and method of the present invention is alsoapplicable to non-destructive testing/evaluation (e.g., pipelinetesting, airframe testing, turbine blades testing, bridge and structuraltesting, manufacturing testing (e.g. metal working rolls)) Ultrasonictesting is a type of nondestructive testing commonly used to find flawsin materials and to measure the thickness of objects. Frequencies of 1to 50 MHz are common but for special purposes other frequencies areused. Inspection may be manual or automated and is an essential part ofmodern manufacturing processes. Most metals can be inspected as well asplastics and aerospace composites. Lower frequency ultrasound (50-500kHz) can also be used to inspect less dense materials such as wood,concrete and cement. The system and method of the present invention isalso applicable to geophysical exploration and sonar applications, andgenerally any ultrasound imaging (or image-like) applications requiringbeamforming for transmission and/or receiving. The present invention isdirected in particular the way signals coming from the elements of anultrasonic array (receive beamformer) and going to the elements of thesame array (transmit beamformer) are treated. The invention describes animproved beamformer system that provides better image quality combinedwith significant reduction in systems' size, power consumption andproduction cost as compared to current systems. Thus, even though themain area of application of this invention is in medical ultrasound,this beamforming architecture and the hardware and software built uponits principles can be used in other areas such as non-destructivetesting, sonar, radar, terahertz, infrared, optical imaging systems orfor seismic geophysical exploration, just to name a few examples.

The general idea of the new design is to create a mixed beamformer thatwould use digital control and manipulation of analog signals from thetransducer array elements. Such design allows radical minimization ofthe hardware volume and power consumption of electronic circuitry,opening a possibility for the development of portable and ultraportableultrasound machines as well as advances in premium systems, as describedin detail below.

FIG. 3 depicts a schematic outline of a proposed new type of thebeamformer. In the beamformer of the present invention, an analog signal108 from the element 107 of the array 106 goes through a voltagecontrolled amplifier (VCA) 110 to compensate the signal attenuation inthe media, then is written into an array 131 of Sample-Hold Cells and ata certain sampling rate as a sequence of voltage levels. The samplingrate may be fixed or variable and also may be independent and differentfrom the sampling rate of the reading from the sample hold cells ofarray 131.

Each SHC array 131, also known as Analog Random Access Memory (ARAM)array 131, consists of a plurality Sample/Hold Cells 150 arranged indistinct rows or banks 132 and that have common signal lines and controlswitches that function in a fashion similar to conventional digitalrandom access memory as it will be discussed below. Next, in each signalchannel 109, one Sample/Hold cell 150 of one row 132 is selected inaccordance with the beamforming algorithm and the samples of analogsignal 134 from all channels participating in the beamforming process atthis particular time moment, also known as beamforming instance whichbeing defined as one sampling step in execution of the beamformingalgorithm, are summed by an analog summing circuit 136. The outputanalog signal 138 which represents the results of the beamforming as asequence of analog samples is digitized by the analog-digital converter120 and output data 122 is written to the memory for further processing.

In other words, the beamforming process consists of storing analogsamples of continuous signals from array elements, then reading thecontent of certain analog memory cells in the same way that digitalmemory cells are read in the digital beamformer process. However,instead of adding digital representations of signals to produce theoutput beamformed signal, the analog representations of the same signalare summed up first and the result is digitized. Thus, the process ofoperating samples of analog signals in a digital manner comprises theessence of the Analog Store—Digital Read (ASDR) ultrasound beamformersystem and method of the present invention.

In order to describe the functions and operations of the AnalogStore—Digital Read (ASDR) ultrasound beamformer the description willbegin with the basic building blocks of such the device and progress upto the system level.

Sample—Hold Cell

The basic building block of the analog memory array is a Sample-HoldCell (SHC). The design of SHC is well known and comprises the prior art.Here a SHC design is used based on the storage capacitor as an exampleof the design; however, any device that can store an analog quantity canbe used for building such a cell.

The schematic organization of a single sample-hold cell (SHC) 150 isshown on FIGS. 4A-D and 5. Main elements of the SHC are the storagecapacitor 152, analog switches 154, 156 and 158 that connect capacitor152 to input analog signal line WRITE 160 and output signal lines READ A162 and READ B 164, or to the ground. Switches 154-158 can be made basedon transistors, MEMs, or other technology enabling analog switching andmultiplexing.

FIG. 5 illustrates schematic representation of variations in the basicSHC 150 design, such as the use of one multi-position switch 166, anaddition of bleed resistor 168 to control the acapacitor dischargingprocess or the removal of the READ B signal line, and joining the bottomplate of the storage capacitor 152 permanently to the signal ground.These or any other variation of the SHC design are included as priorart.

The SHC 150 working cycle, shown schematically in FIG. 6, consists ofthe following operation: writing the voltage level into the storagecapacitor 152, storing the charge, reading the content of the capacitor152, and erasing the content of the storage capacitor 152 inpreparations for the next work cycle. Referring to time diagram of FIG.7, during the write operation at time t_(i), the top plate of thecapacitor 152 is connected to the input analog signal line WRITE 160 viaswitches 154 and 156. Switch 158 connects the bottom plate of the 152 tothe ground. The voltage value of V(t_(i)) from the output of VCA₁ (110)is stored in the capacitor 152. During the time period T₃ (storageoperation), one or both switches 154 and 156 are in a high impedancestate (open or disconnected from signal lines). After time T₃ thatoccurs within the time period T₁, the content of capacitor 152 is read.In the read operation, switch 158 connects the bottom plate of thecapacitor 152 to the READ B output signal line 164 and the top plate ofthe capacitor 152 through switches 154 and 156 is connected to the READA signal line 162. The discharge operation that occurs during timeperiod T₂ consists of connecting the top and bottom plates of thecapacitor 152 via switches 154 and 158 to the ground directly or throughthe bleed resistor 168. The total time of read-store-discharge cycle(referring to FIG. 7) Δt=t_(i+1)−t_(i)=T₁+T₂ is defined by the length ofthe rows (number of S/H cells) of SHC bank 109, sampling rate, and themaximum signal delays need to be corrected.

The open and close state of switches 154-158 is controlled by thebeamformer control circuitry that will be discussed below.

Sample-Hold Cell Array

The separate sample-hold cells 150 are organized row-wise andcolumn-wise into the Sample-Hold Cells Array 131 (or an analog randomaccess memory or ARAM). In the preferred embodiment the number of rows132 of the array 131 (or a number of beamformer channels 109) istypically equal to the number of elements 107 in the transducer array106 (for example 128 elements). In other embodiments, the number ofbeamforming channels 109 can be smaller or larger that number. Thenumber of columns (number of S/H cells in SHC bank 132) is defined bythe sampling rate and the maximum delay in signal arrival to theelements of the transducer array 106 as it will be explained later.

For example, for a common curved medical ultrasound transducer arraylike that known as C5-2/60 with a fully opened active aperture of 128elements (total length of 60 mm) and the signal penetrated into thetissue to z=100 mm depth, the maximum signal path difference (a pulsecoming from the depth z to the center of the aperture and to theaperture edge) will be around Δd≈4.4 mm (see FIG. 3 for the reference).At a sound speed of 1540 m/s, it gives maximum delay Δt≈2.86×10-6s. Atthe sampling rate of S=40 MS/s (mega samples per second) it will benecessary to capture a minimum 114 sample points to be able tocompensate for the 2.86 micro-seconds delay in arrival of signals to allelements 107 of the aperture. Thus, in this particular case, the SHCarray 131 will consist of at least 114 columns of sample-hold cells 150in each of 128 rows 132. In other embodiments the number of columns Ncan be bigger than the minimum required number, but the criteria N>Δt×S(Samples/sec) gives the minimum estimate for the number of samplecapacitors or cells 150 in each row 132.

Column-wise organization of the SHC array is used for writing data intothe S/H cells 150 and row-wise organization is used to read data out ofthe cells. In FIGS. 8A and B, two main architectures/methods to employsuch an array in an ultrasound beamformer are shown. FIG. 8A displays apartial schematic diagram of one channel 109 of an ultrasound system inwhich a SHC row 132 is shared between the transmit and receivebeamformer channel via switch 184 and FIG. 8B shows a partial schematicdiagram of one ultrasound channel 109 where transmit and receivebeamformers have their own SHC row banks 132 and 133 to store and readanalog samples. Note, that even though banks 132 and 133 may have thesame design (as shown on FIGS. 4A-D and 5), the SHC bank 133 is markedseparate from the 132 just to denote that they belong to two physicallydifferent arrays that may have different size and different values ofstorage capacitors 150. All S/H cells 150 that belong to the row bank132 are connected to common signal lines 160, 162, and 164. The logiccircuits that control cells switches 152-158 allow selection of a singlecell, a group, or all cells to perform read, write, store, or dischargeoperations in a similar fashion to the logic that controls the digitaldynamic RAM operations.

Transmit Beamformer Operations

Referring to the FIG. 8B, the transmit phase of beamformer operationsbegins with writing a pulse shape into the beamformer channel transmitanalog sample storage 133 in which the Digital Analog Converter or DAC(not shown) uses WRITE line 160 to write voltage level samples intocells 150 of SHC row 133. The preferred embodiment is to have a numberof transmit beamformer channels 133 be equal to the number of receivechannels 132 and the number of the transducer array elements 107. Inother embodiments, a number of transmit channels can be bigger than thenumber of array elements for storing different signal shapes or smallerthan the number of elements 107 down to a single channel 133 serving allelements of the array. The pulse shape is formed by a sequence ofvoltage samples stored in 133. In order to form the pulse, sample-holdcells 150 of SHC row 133 are sequentially connected to the input of highvoltage pulser 182 that is in turn connected to the transducer element107 via transmit-receive switch 180. The pulse central frequency and thefrequency content are defined by the pulse shape together with thesampling (or clock) speed at which voltage samples arrive to the inputof the pulser 182. The beamforming delay for the each transmit channelis formed by the channels' own hardware or software timer that delaysthe start of pulse forming by an appropriate number of clock cyclesusing for example a countdown counter or buffer.

In one embodiment, the voltage resolution of the sample-hold cells inthe SHC row of transmit channel 133 can be lower than the SHC resolutionin the SHC row of receive channel 132. In other embodiments, transmitchannel cell resolution can be as low as 2 bits or be as high as thereceive SHC resolution. The depth of the transmit SHC row 133 can varyfrom two cells to the number equal of the number of cells in the receiverow 132.

The SHC row 133 may store not one but a number of pulse shapessequentially, that can be rapidly selected by the transmit controller toform different pulses during the current scan line operation (forinstance to form multiple focus points in one scan line generation withvarious central frequency pulses) or for a different scan linesgenerations (for example as in pulse inversion imaging).

In one embodiment, each SHC row 133 may store a pulse shape that iscommon for all beamforming channels or store a pulse shape that isindividual for each beamforming channel or groups of beamformingchannels.

The pulse shapes can be refreshed or re-written during the receive phaseof beamforming if required. The clock or sampling frequency of thetransmit beamformer circuitry can be the same as clock speed of thereceive beamformer or be different from it, either higher or lower—i.e.they are independent. Further the sampling frequency may be variable. Inone embodiment, the sampling speed of the transmit beamformer can bechanged programmatically while in transmit to change the frequencycontent of the transmit pulse while preserving its' recorded shape.

The other possible embodiment of transmit-receive channel architectureis shown in FIG. 8A. In this embodiment, transmit and receive parts ofbeamforming channel share the same SHC array 132 via switch 184. Thetransmit and receive operation in this embodiment proceeds in the samefashion as it was described above with the exception that at the end ofreceive cycle the WRITE line 160 is disconnected from the output of 110and a pulse shape data from the external DAC is written sequentiallyinto SHC cells of array 132 while the last receive beamforming eventsoccur in the far end of the SHC array.

Receive Beamformer Operations

Referring to the schematic of the beamforming channel 109 on FIG. 8B,the piezo-element 107 (part of the transducer array 106) convertselectric energy into mechanical vibrations during the transmit stage andmechanical vibration energy into electric signals during the receivestage. The transmit-receive switch 180 connects the element 107 to theoutput of high voltage transmit pulser 182 or to the input of theamplifier 110 (that may internally consist of a low-pass filter, a lownoise amplifier (LNA) stage and a VCA as a second stage for time-gaincompensation). The filtered and amplified signal from the output of theVCA 110 is connected to the WRITE signal lane 160 that connects allsample-hold cells 150 that form the SHC row 132. Instead of the outputof VCA 110, the signal line 160 can be connected via switch 188 to thereference voltage source 186 which allows testing the performance andcalibration of cells in the bank 132 by writing and reading thecalibrated voltage levels. Output READ signal lines 162 and 164 allowconnecting any storage capacitor of any cell 150 to the input of thecurrent or voltage follower or a summing circuit or allow to directlyconnect selection of storage capacitors 150 sequentially when noapodisation is required (for example, in sub-aperture beamforming).

During the receive stage, voltage levels from VCA 110 are sampled with acertain frequency (sampling rate) and stored in consecutive cells 150until the last cell has received a sample to store. At that point, thewrite operation starts again with the first cell (proceeding by the celldischarge operation as shown in FIGS. 6 and 7). In some embodiments thedischarge operation may not be included and the old cell's content issimply replaced by the new one during the write operation. The writingoperation begins at the moment when the signal scattered from theminimum depth set by the user reaches the array and continues until thesignal from the pre-set maximum depth comes to the farthest element ofthe array participating in beamforming. However, instead of writing andstoring the whole time-pressure history for all elements of array in thecourse of receiving scattered data for the creation of a scan line, thepresent invention uses a sliding window approach, storing only thecurrent part that is used in the creation of current samples of thebeamformed signal.

After the start of data acquisition and filling enough columns, thereading (beamforming) operation begins. FIG. 9 illustrates how thewriting to and reading from the SHC array occurs. In it, each squarerepresents one sample-hold cell 150 with N rows (beamforming channels)and M columns Δt time instance t_(J+1) samples of voltage levels fromcorresponding VCAs 110 are written into column 210 marked by the symbolW₁. At the same time, cells 214 marked by R₁ are selected by thebeamforming algorithm for a creation of the current output beamformedsample. The content of these cells is read and summed by a summingcircuit. At the next sampling interval time t_(J+2) S/H cells 212 markedby W₂ are written and cells 216 (R₂) are read. When the read operationreaches the end of the SHC array it folds over to the first column, inthe same way as the analog sample write operation does. Since thepresent system has separate signal lines for read and write, theseoperations could be done simultaneously. It is desirable to keep thenumber of columns in the array a bit bigger than the minimum numberrequired, so the read and write operation would not overlap. In someembodiments the system divides the whole array 131 column-wise into afew independent blocks allowing a write operation in one column-wisememory block, discharge in the next one, while the rest of blocks isreserved for the read operation. For instance, the system dividescolumn-wise the array 131 consisting of 128×128 elements into eightblocks of 128×16 SHC cells each. Then, at some moment of time block 5 isused for writing data from 128 channels, block 6 for discharging it'scontent, and blocks 7,8, 1-4 are used for reading and beamforming. Thisway we can use a segmented single signal line for accessing the cellsinstead of separate read and write lines.

The freedom in selecting which cells would participate in thebeamforming instance allows reusing the stored sampling data toimplement not just a single beamforming algorithm, but obtain a numberof various beamforming scenarios on the same block of data, similarly asit can be performed with stored channel data in digital beamformingarchitecture.

Generally speaking, write operations do not need to be performed onconsecutive columns of S/H cells. The cell's addresses can be random aslong as the memory controller keeps the score. Writing data column-wiseis a convenient option, however SHC arrays can be also built to be usedas truly random access analog memory ARAM with voltage level samplesfrom an element being stored in random locations (no hard channel andtiming links). Potential advantages of that approach are enablingfreedom to choose the depth of SHC row banks (channels) and size ofaperture (number of rows or transducer elements). Among potentialdisadvantages-analog multiplexors are needed to switch channels and thewriting speed may be lower, however, such a design option may beconsidered for some applications.

Also, sampling rates for Sample-Hold Cells array 132, summator 136 andADC 120 does not need to be the same and/or be synchronized. In someembodiments it may be desired to have a single clock to control allthree blocks, in other embodiments it may be desired to have a phasedifference between read, write and digitize operation. In yet anotherembodiment it may be desired to have different frequencies phase-linkedor completely independent, to control the operation of Sample-Hold Cellsarray 132, summator 136 and ADC 120. There may be benefits (e.g.,anti-aliasing) to have all three functional blocks functioning atindependent sampling rates with different frequencies and phases. Forinstance, writing data 108 from the elements 107 could be done at 100mega samples per second, reading data 134 for summation 136 at 85 megasamples per second and digitizing by ADC 120 at 60 MS/s.

Receive Beamforming Summing Operations

The beamforming summation can be done with voltage or with currentvalues of analog samples stored in SHC 150. Referring to FIGS. 9 and 10,in the beamforming instance at time t_(J+1) after cell 150 (marked byR₁) in each beamforming channel 132 was selected by the beamformingalgorithm, the storage capacitor 152 is connected to the input ofvoltage or current follower 200 by signal lines READ A (162) and READ B(164). In one embodiment, the voltage follower 200 is connected tovoltage controlled amplifier 202 that is used for forming of apertureapodization and for capacitor calibration compensation. The currentactive aperture span is controlled by setting apodization value to zerofor the channels that will not be participating in current beamforminginstance. In another embodiment, voltage follower 200 and VCA 202 can becombined in one circuit. In yet another embodiment, 200 is a currentfollower. In another embodiment one plate of storage capacitor 152 ispermanently attached to the signal ground and signal line READ B 164 isabsent.

In one embodiment each receive beamforming channel has its own 200 and202 amplifiers. Another embodiment may have a reduced number of 200 and202 amplifiers and have analog multiplexors to connect the selectedbeamforming channels with the aperture formed by the multitude of 200and 202 amplifiers. Yet another embodiment may have VCA 202 be removedor be replaced by an analog switch for active aperture selection.

For the convenience, the system defines the analog channel AC 203 thatincludes all of the elements and functional blocks that participate inthe analog signal acquisition, storing and processing from the output ofarray element 107 to the voltage sample on the output VCA 202. Output ofVCA 202 (or AC 203) represent a properly delayed, apodized andcompensated analog channel sample.

In the voltage summing scheme, the summing circuit 136 receivesinstances of voltage samples from all beamforming channels, sums themand outputs the result. If the current summing approach is used, thecircuit 136 is the current summing circuit. In another embodimentsumming is achieved not with the content of actual storage capacitors152 but their content first copied into temporary storage capacitorsthat are used for summing. In yet another embodiment, summing isachieved by connecting all storage capacitors 152 or temporary storagecapacitors participating in the beamforming event serially in which line164 of the first capacitor is connected to line 162 of second rowcapacitor etc. until the last capacitor is connected. The sum value thenread from line 162 of the first capacitor and line 164 of the lastcapacitor.

The output of the summing circuit 136 is connected to a secondarySample-Hold Cell 204, VCA 206, and Analog-Digital Converter 120. Theoutput of analog digital converter 120 is a digitized beamformed RFsignal. Elements 204 and 206 may be absent from the schematic, beattached in reverse order, or be internal elements of ADC 120. The VCA206 may include a low pass filter.

In one embodiment, in-phase/quadrature (I/Q) data is generated bydirectly sampling the received radio frequency (RF) signal from theoutput of ADC 120. In another embodiment the output of VCA 206 also maybe connected to a conventional I/Q demodulation sampling circuit.

Secondary SHC

The secondary Sample-Hold Cell 204 has the same design as S/H cell 150.In one embodiment a single SHC 204 is used to store the current resultsof summing in element 136. In another embodiment, as shown on FIG. 11, anumber of S/H cells can be used for temporarily storing results ofsumming the different beamforming algorithms working on the samechannel's data block before their analog to digital conversion viaswitch 208 and secondary VCA 206 (VCA may be absent or replaced by avoltage follower). In yet another embodiment, the secondary SHC arraymay have a similar size and a similar use to the primary SHC array 131.In it, primary array 131 is used for sub-aperture beamforming, operatingon the group of closely spaced transducer elements and the secondary SHCarray is used for beamforming the results of pre-beamforming asdescribed below. In yet another embodiment there may be a tertiary SHCarray working on results of sub-aperture beamforming of the secondarySHC array and so on.

1.5D, 1.75D, 2D Arrays Operation

The beamforming architecture described above can accommodate any common1D ultrasound arrays with number of elements (transmit-receive channels)in array going up to a few thousand (refer to FIG. 12A schematicallypicturing layout of a common 1D array). With a larger element count orwith a more complicated structure of the transducer array, being 1.5D,1.75D, or 2D, this basic architecture can be adapted in the waypartially described above (secondary Sample-Hold Cell array). Referringto the top schematic of FIG. 12, the typical 1.5D or 1.75D array isessentially a 1D transducer that has its elements divided in elevationdirections with each element preferably having separate beamformingchannels. The number of divisions can be any, however when the size ofthe sub-element in elevation direction (Y-axis on the figure) approachesthe size in axial direction (X-axis) and both sizes being equal or lessthan half of wavelength of the array's central frequency, it is moreproper to describe such array as a 2D array (referring to lowerschematics of FIG. 12 correspondingly). The main reason for using suchan array is that it allows controlling focusing in elevation directionin the same way the axial focusing is controlled, thus, providingconstant image slice thickness in elevation with correspondingimprovements in contrast and detail resolution.

The main difference between 1.5D and 1.75D arrays is that in 1.5D arrayelements are connected symmetrically column-wise (referring to FIG. 12)so the elevation focusing is done only in the plane of the image sliceor in the Y-Z plane (Z-axis being a depth and directed perpendicular tothe FIG. 12 plane) while 1.75D array sub-elements are controlledindependently, thus, a limited out-of-plane focusing can be performed,restricted by the grating lobes position. The 2D array, with itselements being close to ½ wavelengths, has the same freedom in focusingin all three directions: elevation, axial, and depth.

In the preferred embodiment for 1.5D, 1.75D, and 2D arrays, all elementsof the array are divided into groups or sub-apertures 218. Some examplesof such sub-apertures are shown on the lower schematics of FIG. 12. Thepreferred way to select sub-aperture is to assemble an array's elementsbased on the minimum group delay with respect to the sub-aperture'scentral element (example on the lowest schematic of FIG. 12) allowing asmall number of sample-hold cells in the receive beamformer channel 132of primary analog channel 203 (FIG. 13), where under the primary (orfirst) analog channel we understood the channel that connected to thearray element. The elements of sub-aperture 218 connect to analogchannel 203 (with smaller number of SHC 150) then the content of cells150 from different channels within sub-aperture is beamformed in the waydescribed above and the output of summing circuit 136 is connected tothe second stage beamformer channel 135 which has the same design asbeamformer channel 132, but numbered differently to show that first andsecond stage beamformer channels 132 and 135 are physically differentdevices that might have different internal structure (e.g. number ofcells 150). The contribution of 135 is summed by the second stagesumming circuit 137. The output of 137 is the beamformed analog signalput to the input of analog digital converter 120 to create a digitizedbeamformed RF signal. It is understood that this invention allows forany number of sub-aperture to be formed.

It is also understood that this invention allows for any number ofbeamforming stages to be implemented, where each collected contributionof lower level sub-apertures become a single channel in the next levelsub-aperture until a single beamformed signal is outputted.

In one embodiment for 1.5D, 1.75D, and 2D arrays, all beamforming isdone in the ASDR beamformer hardware placed next to the array. Inanother embodiment, some sub-aperture beamforming could be done in ASDRbeamformer next to the array, and then partially beamformed signals aresent via wire or wireless link to the ultrasound machine hardware wherethe final beamforming is done in ASDR beamformer or in the prior artdigital beamformer. The main advantage of such approach is the reductionin number of cables running from the probe to the ultrasound hardware.

Portable Ultrasound Device and ASIC Structure

The ASDR beamformer described in this invention can be used to buildcompact ultrasound diagnostic devices that combine small size and powerconsumption with high image quality that results from the high channelcount of full aperture and short signal path 109. Such system can beimplemented as system-on-the-probe where all hardware necessary forsignal acquisition and processing fits in the transducer array handletogether with the battery, which wirelessly transmits beamformed andprocessed signals to the receiver that is connected to a display unitsuch as a laptop, smartphone, tablet, or a TV set where images aredisplayed.

In one embodiment of such a diagnostic ultrasound system, as it is shownon the example of schematic diagram on FIG. 14, the ASDR beamformer isimplemented as one or few integral chips (ICs) that are placed inimmediate vicinity of the transducer array 106. Functioning of the Nchannels (equal to the number of elements) receive beamformer 252 wasdescribed above. In it, the signal from each element of array 106through T/R switch 180 goes to VCA 110, S/H cells bank 132, then thevoltage level of the selected SHC elements through the follower 200 goto the input of summing circuit 136 and via VCA 206 go to the input ofADC 120. The digitized data from the output ADC are written in buffermemory 254.

The transmit-receive control circuitry block 256 controls the flow ofdata and command in and out of receive beamformers 250, 252, buffermemory 254, and back-end processor 258.

The transmit beamformer 250 writes voltage levels from digital-to-analogconverter 242 via buffer amplifier 240 to the transmit SHC array 133.The voltage level samples from 133 are sequentially sent to the pulser182 to form the high voltage pulse that is sent to the transducer array.The transmit beamforming delays are controlled by the T/R controlcircuitry block 256. The transmit beamformer DAC 242 may refresh thecontent of array SHC 133 while the Rx beamformer is in receive mode.

The back-end processor 258 performs initial signal and image processingon raw RF data received from the buffer memory including but not limitedto data flow organization (such as creation of line and frame headers),filtering, I/Q, B-mode conversion, Doppler data extraction, datacompression, scan image forming, and other typical tasks of the back-endDSP. It also receives and interprets the commands from any buttons androtary dial controls of the ultrasonic hardware control block 260.Another task of the processor 258 is to organize the flow of informationto the outside storage and processing interface block 262, that controlswriting ultrasound data to the non-volatile memory storage (such asflash card, SD or a micro-SD), wire based data transfer (such as USB)port and wireless data interface.

The scan data (such as raw RF, Doppler, B-mode, image, volume data) aretransferred outside from the probe-side hardware block 264 via wire linkor wireless link 266 to the display-side hardware block 270. There, datadecoded by the interface 272, the image processed in the block 274 tofit the format of the current display device and outputted to thedisplay interface 276 that transmits the data in the format accepted bythe display device through USB, HDMI, DVI, or another input signal port.

In one embodiment of such a system, the ASDR beamformer is built on oneASIC that along with the analog front-end, SHC arrays, digital back end,and control circuitry may include all functional blocks described inblock 264 with the exception of the transducer array. In anotherembodiment, some of the functional blocks or parts of such blocksdescribed in block 264 may be realized separately from the ASDR ASIC. Inanother embodiment, the system may consist not from a single ASDR ASICbut from a few independent ASDR beamformers working on the single ADC(or each on their own ADC) where each ASDR beamformer has a part of thearray 106 as its sub-aperture and final beamforming is done digitally ondata streams coming from the multitude of ASDR beamformers. In yetanother embodiment few independent ASDR beamformers can be working onthe same array 106 with time interleave to achieve higher samplingrates.

It should be noted that the beamformer system is implemented partiallyin hardware, partially in firmware and partially in software such thatprecise boundaries between these parts can be established by the needsof the implementation. Further, in all descriptions and schematicdiagrams the placement of elements or blocks such as VCA, LNA, voltagefollowers switches, etc. that are secondary to the understanding of theinvention are not strictly followed, assuming that anybody with ordinaryknowledge of electronic design would understand their functions woulddetermine where they should be placed in the actual working schematics,their structure, and parameters.

The above description describes an Analog Store Digital Read ultrasoundbeamforming method for an ultrasound imaging system comprising the stepsof: i) Providing an ultrasonic array formed of individual ultrasonicarray elements configured for transmission and receiving; ii) Dividingthe individual array elements into individual channels, wherein eachchannel comprises at least one array element; iii) Creating a receivinginput signal for each channel from inputs received from each arrayelement of the channel; iv) Sampling each receiving input signal foreach channel at a sampling rate and storing the sampled data in a bankof sample-hold cells which are associated with that channel, wherein thebank of sample-hold cells form an analog random access memory for thesampled receiving input signal; v) Selecting at least one sample-holdcell data from at least one channel for each particular output time foreach beamforming instance in accordance with a beamforming algorithm;vi) Summing all of the selected sample-hold cell data from theassociated channels for the beamforming instance forming an analogbeamformed received signal sample for the beamforming instance; and vii)Digitizing the analog beamformed received signal sample.

CONCLUSION

As discussed above the individual channels will generally include, notjust the array elements but also the control electronics. Further it isimportant to note the sampling rate may be fixed or may be variable andmay further be independent of the rate the data is read from the cellsor the rate such is digitized. The digitized sample is typically storedfor further processing as known in the art.

In the Analog Store Digital Read ultrasound beamforming method for anultrasound imaging system, each channel may comprise only one arrayelement. Further, the creating a receiving input signal for each channelmay include processing the inputs from the array elements through atleast one voltage controlled amplifier and at least one filter.Additionally, each channel may use less than 40 milliwatts in operation,generally less than 25 milliwatts per channel and typically about 10milliwatts per channel or even less. Each sample-hold cell may be formedas a capacitor based element. It is noteworthy that selected sample-holddata pass through an analog filter or/and amplifier with variable gainwith purpose to assign proper Time Gain Compensation (TGC) values,aperture selection and apodization weighting before the summing forproper signal to noise attenuation.

In the Analog Store Digital Read ultrasound beamforming method thenumber of sample-hold cells in each bank may be equal to or greater thanthe sample rate per second times the maximum desired delay for thesignal path. Further, a sampling speed for the storing of the sampleddata in the bank of sample-hold cells may be independent of a samplingspeed for reading the sampled data in the bank of sample-hold cells.

The Analog Store Digital Read ultrasound beamforming method may furtherinclude the step of storing at least one shape of a transmission outputpulse signal for each transmission channel in a bank of transmissionsample-hold cells which are associated with that transmission channel.In one embodiment a single bank of transmission sample-hold cells areassociated with multiple transmission channels. Further the method mayprovide that the same bank of sample-hold cells forms the receiving bankof sample-hold cells and the bank of transmission sample-hold cells foreach channel. Alternatively, each channel may be associated with onereceiving bank of sample-hold cells and one distinct bank oftransmission sample-hold cells.

The Analog Store Digital Read ultrasound beamforming method for anultrasound imaging system as described above provides that multiplebeamforming instances associated with multiple algorithms may beutilized, and may further include the step of storing each of the analogbeamformed received signal for each beamforming instances in a bank ofbeamform sample-hold cells prior to digitizing the analog beamformedreceived signals.

As summarized above, there are two ways to organize sample memory: 1)During the operation the data are written continuously into the ARAMorganized as a ring buffer, such that when the current sample is writteninto the last address, the write operation folds and begin writing atthe first address of the array; or 2) The ARAM memory depth issufficient to store the whole length of the channel data for the scanline (here the maximum delay is the time required for the signal totravel to the maximum desired scan depth and back to the receiver)providing greater freedom for multiple beamforming

The above description defines the transmit beamforming essentially thesame way as it describes the receive beamforming. In short a transmitbeamformer that forms an ultrasonic pulse by sequentially reading analogsample values stored in transmission bank of sample-hold cells inchannels selected by the beamforming algorithm, sending them to the highvoltage amplifier or generator connected to the elements of thetransmit—receive array where each channel begin to read analog samplevalues with predefined time delays and sampling rates in accordance tothe transmit beamforming algorithms

The above description sets forth an Analog Store Digital Read ultrasoundbeamformer for an ultrasound imaging system comprising: i) An ultrasonicarray formed of individual ultrasonic array elements configured fortransmission and receiving, wherein the individual array elements aregrouped into individual channels, wherein each channel comprises atleast one array element; ii) A Receiving input signal control circuitryfor creating receiving input signals for each channel from inputsreceived from each array element of the channel; iii) A plurality ofbanks of sample-hold cells with each bank of sample-hold cellsassociated with one channel, wherein the beamformer is configured forsampling each receiving input signal for each channel at a sampling rateand storing the sampled data in one bank of sample-hold cells which areassociated with that channel, wherein the bank of sample-hold cells forman analog random access memory for the associated sampled receivinginput signal; iv) A beamforming processor configured for selecting atleast one sample-hold cell data from at least one channel for eachbeamforming instance in accordance with a beamforming algorithm; v) Ananalog summation element for summing all of the selected sample-holdcell data from each channel for each beamforming instance and forming ananalog beamformed received signal for the beamforming instance; and vi)An Analog-to-Digital converter for digitizing the analog beamformedreceived signal.

At least the beamforming processor may be formed as an integratedcircuit. Essentially the circuitry implementing the beamforming methodmay comprise an integrated circuit (IC) such as an application-specificintegrated circuit (ASIC).

The above description also defines an Analog Store Digital Readultrasound beamforming system for an ultrasound imaging systemcomprising an ultrasonic array formed of individual ultrasonic arrayelements configured for transmission and receiving, wherein theindividual array elements are formed into individual channels, whereineach channel comprises at least one array element and each channel usesless than 40 milliwatts in operation, and generally less than about 25milliwatts per channel, often less than 15 milliwatts per channel oreven less than 10 milliwatts per channel.

The compact ultrasound imaging system formed according to the presentinvention may send the beamformed signal to an outside display devicewirelessly or wired in a display neutral system or manner. The systemdescribed provides a compact ASIC, low power device and high channelcount (128 or more), with simple scalable architecture. It should beapparent that the beamformer system is implemented partially inhardware, partially in firmware and partially in software such thatprecise boundaries between these parts can be established by the needsof the implementation.

Further regarding, Sub-aperture beamforming and the secondarySample-Hold cell bank described above, first, second and tertiary levels(any number of beamforming stages) of sub-aperture beamforming usingARAM beamforming may be provided. An effective way to selectsub-aperture is to assemble an array's elements based on the minimumgroup delay with respect to the sub-aperture's central element. Thesystem may be mix of beamformer methods ARAM, analog, digital fordifferent stages of sub-aperture beamformer. Further the stages ofbeamforming can be spatially separated (first stage on the probe andsecond on the hardware side)—

One advantage of the invention is that it provides significant reductionin the size of the diagnostic ultrasound imaging system such that thehardware build upon ASDR ultrasound beamformer architecture can beplaced in one or few application specific integrated chips (ASIC)positioned next to the ultrasound array and the whole diagnosticultrasound imaging system could fit in the handle of the ultrasonicprobe while preserving most of the functionality of a cart-based system.

Another advantage of the invention is that such compact system allowssending data and diagnostic images wirelessly to any image displayequipped to receive such transmissions or having such a receiverattached to data ports such as USB or FireWire of the display unit.

Another advantage of the invention is that it provides an improvedsignal-to-noise ratio by drastic reduction in hardware complexity of thesignal path from the transducer elements to the digitizer. Such ashortening of the signal path is achieved by making redundant a numberof components of the signal path such as analog high voltage and channelmultiplexors, signal cable, and connectors used in prior art to connectultrasound array with signal processing hardware.

Another advantage of the invention is that it further improves thesignal-to-noise ratio, and diagnostic image contrast, and spatialresolution by implementing the full aperture beam formation in whichevery element of the array operates its' own transmit and receivechannel (128 parallel transmit-receive channels for a typical 128elements 1D array) and thus, the available aperture is equal to the sizeof the whole array.

Another advantage of the invention is that it uses lower power perchannel, thus, allowing for extended time operation on battery power.

Another advantage of the invention is that implementation in one or fewASICs significantly reduce the cost of production of ultrasound system.

Another advantage of the invention is that it has scalable architectureenabling the construction of ultrasound arrays with any number ofelements by linear expansion (e.g. one ASIC controls 128 element 1Darray, two ASIC—256 elements array, and so on)

Another advantage of the invention is that it improves image quality andreduces the cost of systems built with 1.5D, 1.75D and 2D arrays.

Although the present invention has been described with particularityherein, the scope of the present invention is not limited to thespecific embodiments disclosed. It will be apparent to those of ordinaryskill in the art that various modifications may be made to the presentinvention without departing from the spirit and scope thereof. Forexample the array may be selected in length to provide a whole-scan-linechannel storage option, which would not change the fundamentals ofoperation of the system or method of the invention.

What is claimed is:
 1. An Analog Store Digital Read ultrasoundbeamforming method for an ultrasound imaging system comprising the stepsof: Providing an ultrasonic array formed of individual ultrasonic arrayelements configured for transmission and receiving; Dividing theindividual array elements into individual channels, wherein each channelcomprises at least one array element; Creating a receiving input signalfor each channel from inputs received from each array element of thechannel; Sampling each receiving input signal for each channel at asampling rate and storing the sampled data in a bank of sample-holdcells which are associated with that channel, wherein the bank ofsample-hold cells form an analog random access memory for the sampledreceiving input signal; Selecting at least one sample-hold cell datafrom at least one channel for each particular output time for eachbeamforming instance in accordance with a beamforming algorithm; Summingall of the selected sample-hold cell data from the associated channelsfor the beamforming instance forming an analog beamformed receivedsignal sample for the beamforming instance; and Digitizing the analogbeamformed received signal sample.
 2. The Analog Store Digital Readultrasound beamforming method for an ultrasound imaging system accordingto claim 1 wherein each channel comprises only one array element, andwherein the creating a receiving input signal for each channel includesprocessing the inputs from the array elements through at least onevoltage controlled amplifier and at least one filter, and wherein eachchannel uses less than 40 milliwatts in operation.
 3. The Analog StoreDigital Read ultrasound beamforming method for an ultrasound imagingsystem according to claim 1 wherein each sample-hold cell is formed as acapacitor based element and wherein each channel uses less than 25milliwatts in operation.
 4. The Analog Store Digital Read ultrasoundbeamforming method for an ultrasound imaging system according to claim 1wherein the number of sample-hold cells in each bank is equal to orgreater than the sample rate per second times the maximum desired delayfor the signal path, and wherein a sampling speed for the storing of thesampled data in the bank of sample-hold cells is independent of asampling speed for reading the sampled data in the bank of sample-holdcells.
 5. The Analog Store Digital Read ultrasound beamforming methodfor an ultrasound imaging system according to claim 1 further includingthe step of storing at least one shape of a transmission output pulsesignal for each transmission channel in a bank of transmissionsample-hold cells which are associated with that transmission channel.6. The Analog Store Digital Read ultrasound beamforming method for anultrasound imaging system according to claim 5 wherein a single bank oftransmission sample-hold cells are associated with multiple transmissionchannels.
 7. The Analog Store Digital Read ultrasound beamforming methodfor an ultrasound imaging system according to claim 5 wherein the samebank of sample-hold cells forms the receiving bank of sample-hold cellsand the bank of transmission sample-hold cells for each channel.
 8. TheAnalog Store Digital Read ultrasound beamforming method for anultrasound imaging system according to claim 5 wherein each channel isassociated with one receiving bank of sample-hold cells and one distinctbank of transmission sample-hold cells.
 9. The Analog Store Digital Readultrasound beamforming method for an ultrasound imaging system accordingto claim 1 wherein multiple beamforming instances associated withmultiple algorithms are utilized, and further including the step ofstoring each of the analog beamformed received signal for eachbeamforming instances in a bank of beamform sample-hold cells prior todigitizing the analog beamformed received signals.
 10. An Analog StoreDigital Read ultrasound beamformer for an ultrasound imaging systemcomprising: An ultrasonic array formed of individual ultrasonic arrayelements configured for transmission and receiving, wherein theindividual array elements are grouped into individual channels, whereineach channel comprises at least one array element; A Receiving inputsignal control circuitry for creating receiving input signals for eachchannel from inputs received from each array element of the channel; Aplurality of banks of sample-hold cells with each bank of sample-holdcells associated with one channel, wherein the beamformer is configuredfor sampling each receiving input signal for each channel at a samplingrate and storing the sampled data in one bank of sample-hold cells whichare associated with that channel, wherein the bank of sample-hold cellsform an analog random access memory for the associated sampled receivinginput signal; A beamforming processor configured for selecting at leastone sample-hold cell data from at least one channel for each beamforminginstance in accordance with a beamforming algorithm; An analog summationelement for summing all of the selected sample-hold cell data from eachchannel for each beamforming instance and forming an analog beamformedreceived signal sample for the beamforming instance; and AnAnalog-to-Digital converter for digitizing the analog beamformedreceived signal.
 11. The Analog Store Digital Read ultrasound beamformerfor an ultrasound imaging system according to claim 10 wherein eachchannel comprises only one array element, and wherein each channel usesless than 40 milliwatts in operation.
 12. The Analog Store Digital Readultrasound beamformer for an ultrasound imaging system according toclaim 10 wherein each sample-hold cell is formed as a capacitor basedelement and wherein at least part of the beamforming processor is formedas an integrated circuit.
 13. The Analog Store Digital Read ultrasoundbeamformer for an ultrasound imaging system according to claim 10wherein the number of sample-hold cells in each bank is equal to orgreater than the sample rate times the maximum desired delay for thesignal path.
 14. The Analog Store Digital Read ultrasound beamformer foran ultrasound imaging system according to claim 10 further including atransmission beamformer for storing at least portions of onetransmission output pulse signal in a bank of transmission sample-holdcells which are associated with that channel.
 15. The Analog StoreDigital Read ultrasound beamformer for an ultrasound imaging systemaccording to claim 14 wherein a single bank of transmission sample-holdcells are associated with multiple channels.
 16. The Analog StoreDigital Read ultrasound beamformer for an ultrasound imaging systemaccording to claim 14 wherein the same bank of sample-hold cells formsthe receiving bank of sample-hold cells and the bank of transmissionsample-hold cells for at least one channel.
 17. The Analog Store DigitalRead ultrasound beamformer for an ultrasound imaging system according toclaim 14 wherein each channel is associated with one receiving bank ofsample-hold cells and one distinct bank of transmission sample-holdcells.
 18. The Analog Store Digital Read ultrasound beamformer for anultrasound imaging system according to claim 10 wherein multiplebeamforming instances associated with multiple beamforming algorithmsare utilized, and further including a bank of beamform sample-hold cellsconfigured for storing each of the analog beamformed received signalsample for each given beamform prior to digitizing the analog beamformedreceived signals.
 19. An Analog Store Digital Read ultrasoundbeamforming system for an ultrasound imaging system comprising anultrasonic array formed of individual ultrasonic array elementsconfigured for transmission and receiving, wherein the individual arrayelements are formed into individual channels, wherein each channelcomprises at least one array element and each channel uses less than 40milliwatts in operation.
 20. The Analog Store Digital Read ultrasoundbeamforming system according to claim 19 further including i) AReceiving input signal processor in the enclosure for creating receivinginput signals for each channel from inputs received from each arrayelement of the channel; ii) A plurality of banks of sample-hold cells inthe probe with each bank of sample-hold cells associated with onechannel, wherein the beamformer is configured for sampling eachreceiving input signal for each channel at a sampling rate and storingthe sampled data in one bank of sample-hold cells which are associatedwith that channel, wherein the bank of sample-hold cells form an analograndom access memory for the associated sampled receiving input signal;iii) A beamforming processor in the probe configured for selecting atleast one sample-hold cell data from at least one channel for eachbeamforming instance in accordance with a beamforming algorithm; iv) ananalog summation element in the probe for summing all of the selectedsample-hold cell data from each channel for each beamforming instanceforming an analog beamformed received signal for the beamforminginstance; v) An analog-to-digital converter for digitizing the analogbeamformed received signal; and vi) a transmission beamformer forstoring at least portions of one output pulse signal for each channel ina bank of transmission sample-hold cells in the probe which areassociated with that channel.